Your male might not be mature enough yet to spawn, but mine started at about that size. I have noticed that a little bit of a water temperature drop during a water change (about 2 degrees) can encourage things. Give them time though, sometimes they go on and off spawn for no reason at all. I've noticed that the courtship can take a couple of weeks with mine and the first time I watched them go through the motions for three weeks before I had fry.
They're sort of like teenagers that way, moody, but generally willing to try to reproduce.